Lattice parameters δ28, δ25, ρ28 and C* were measured on cluster-type fuel lattices of the ATR (Advanced Thermal Reactor) by using a two region critical facility (D2O-cluster test and H2O-rod driver regions). Their dependence on lattice pitch, coolant-void ratio and fuel composition (whether UO2 or PuO2-UO2) have been made clear by this experiment.A foil handling technique has been developed for determining the lattice parameters of the PuO2-UO2 fuel pins, and the resulting measurement errors are almost as small as those obtained on the UO2 fuel pins.The effects of the Cd-filter and of the presence of UO2 buttons in the measurement of ρ28 and δ25 were studied experimentally and correction factors have been determined.A method of observing the spatial distribution of the γ-ray source in an activated foil has been developed, and the relation between the spatial distribution and the coincidence counting efficiency of the foil has been examined.
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